1. Field of the Invention
This invention pertains to an electronically controlled fuel injection device, and more particularly, to a fuel injection pump controlled by an electronic control unit.
2. Description of the Related Art
A fuel injection pump typically includes an adjusting member for establishing the level of fuel-injection. This adjusting member forms part of an actuator which is activated by signals from a control unit.
Once a target position of the adjusting member is computed by the control unit according to the needs of the engine, the operational level of the actuator is determined to conform the position of the adjusting member to the target position. The aforementioned actuator is secured to the pump with a bolt, and if the actuator is not secured to the pump at an exactly appropriate position, the desired level of fuel injection is not attained.
Therefore, when assembling the fuel-injection pump, prior to tightening the bolt which secures the actuator to the pump, it is necessary to shift the position of the actuator relative to that of the pump to determine the best possible position of the actuator, that is a position in which the desired injection characteristics will be attained.
In the past, the present inventor has proposed the following idea. In order to simplify the task of positioning the actuator relative to the pump, the actuator is first tentatively secured to the pump at a position within a roughly prescribed parameter, a difference between a reference (desired) injection level and an actual injection level is then measured with a pump tester by driving the fuel injection pump through a specific number of rotations, and then an adjustment resistor (Q adjustment resistor) having a resistance value corresponding to this difference is then installed on the fuel-injection pump to correct the difference between the actual injection characteristics and the desired injection characteristics of the fuel-injection pump.
The following similar method is disclosed in Japanese Kokai Patent Publication H2-21594. Data denoting a Q adjustment resistor installed in a fuel-injection pump is read and stored in a memory every time the pump is activated. The data stored in the memory is read to correct those actual fuel injection characteristics of the pump which deviate from desired characteristics. If the Q adjustment resistor operation malfunctions for any reason, an average standard correction value, which has been preliminarily determined as back-up data, is input to the memory. The subsequent control of the fuel injection pump is carried out on the basis of this data.
According to the latter method the actuator is roughly positioned and secured to the pump at such position. Subsequently, the injection characteristics of the pump are minutely adjusted using a Q adjustment resistor. Initially, however, the actual injection characteristics will vastly differ from the reference injection characteristics (the injection characteristics required by engine conditions), since the actuator is only roughly positioned when secured to the pump. Therefore, if the Q resistor does not work, and the back-up data must be utilized, and the difference between the actual and desired injection levels can be as inaccurate as that occurring upon the initial rough positioning of the actuator on the pump. Accordingly, this latter method suffers a drawback in that a large difference can exist between the desired corrected characteristic data of the pump and the back-up data, and thus accurate control of the injection level is impossible when the Q resistor malfunctions.
Additionally, it may be necessary to replace the Q adjustment resistor by trial and error to adjust the actual injection characteristics to agree with desired injection characteristics. Therefore, it is necessary to use a resistor that has a mechanism to correct injection characteristics of the pump according to the required value, every time the Q adjustment resistor is replaced.